Silver salt photography has been known so far as one of many high-sensitivity image pickup techniques. According to this photographic process, a picked-up image is recorded on a film, etc. through a development step and is reproduced as by using a silver salt emulsion (photographic paper, etc. ) or by scanning the developed film optically for display on a cathode ray tube (CRT).
Electrophotography has also been available, in which a photoconductive layer having an electrode applied onto it by vapor deposition is electrified all over its surface by corona charging in a dark place and then exposed to intense light to make the area exposed to light electrically conductive, so that charges can leak out of that area to provide an electrostatic latent image corresponding to the optical exposure on the photoconductive layer. The latent image is then developed by depositing toner at a polarity which is opposite to (or identical with) polarity of the residual electrostatic charges. This electrophotography has been used mainly for copying purposes, but may not generally be applied to picking up images due to its low sensitivity. Due to a short residence time of the charges, it is also required that the toner development be carried out immediately after forming the electrostatic latent image.
A currently available TV image pickup technique is designed to pick up images by an image pickup tube and obtain image information by using an optical semiconductor, which is in turn extracted as an electrical signal and either immediately displayed on a CRT or recorded in a video magnetic recording medium, etc. for display on a CRT at any desired time.
Silver salt photography provides an excellent means for preserving subjects' images: but needs complicated optical, electrical or chemical processings from hard copying to soft copying (CRT output) for reconstructing the images.
Electrophotography is found to be easier and speedier than silver salt photography in terms of developing the electrostatic latent image, but is much poorer in terms of how long the latent image is preserved and much more unsatisfactory in terms of the resolution of a developer, image quality, etc. than silver salt photography.
With the TV image pickup technique, line-sequential scanning is required for extracting and recording electrical image signals. Line-sequential scanning, which is carried out by electron beams in the case of an image pickup tube and by a magnetic head in the case of video recording, is much inferior to such planar analog recording as silver salt photography, because of its resolution being dependent upon the number of scan lines.
This is essentially true of the resolution of a TV image pickup system as well, which relies upon solid-state image sensors (e.g., CCDs) now in the making.
Problems inherent in these techniques are that the higher the quality and resolution of image recording, the more complicated the processing steps involved, or if the processing steps are simple, then there is no room for memory function or the basic image quality degrades.
In the course of having studied methods of recording electrostatic information wherein with a system having on its optical axis a photosensitive member which includes a photoconductive layer provided with an electrode on its front side and a charge carrier medium which is located in opposition thereto and includes a charge carrier layer provided with an electrode on its back side, the information is exposed to light with the application of voltage between both electrodes, thereby forming on the charge carrier medium an electrostatic latent image corresponding to the incident optical image, we have found that a specific photosensitive material itself can function as an excellent recording medium and be used as a novel electrostatic information-recording medium, and so have achieved this invention.
A major object of this invention is to provide a novel electrostatic information-recording medium as well as a method of recording and reproducing electrostatic information, which is applicable to electrostatic printing.